This invention relates to the palladium-catalyzed amination of conjugated dienes with ammonia to produce relatively short chain unsaturated primary and secondary amines.
Organic amines find a wide range of commercial usage such as paper and rubber chemicals, plasticizer intermediates, herbicide intermediates, surfactants, water treatment chemicals and extractants. Because prior methods of preparation are multi-step and sometimes non-selective, amines are a relatively expensive class of chemicals.
The direct addition of ammonia or amines to olefins is a potentially lower cost method of preparing amines. However, such direct addition has been hindered by the high reaction temperatures necessary to meet the activation energy requirements of the reaction and the unfavorable equilibrium thermodynamics for the reactions at these temperatures. One method of overcoming these obstacles is to find a catalyst to lower the energy of activation required and thus allow the reaction to proceed at temperatures where the equilibrium is more favorable.
Direct amination of olefins with amines using soluble palladium catalysts has been reported heretofore by several investigators, for example, Takahashi, Bull. Chem. Soc. Japan 41, 454-60 (1968) and in U.S. Pat. Nos. 3,350,451; 3,444,202; 3,530,187; and British Patent No. 1,178,812. However, the disclosed reactions do not involve ammonia itself and thus do not have the potential for producing primary amines as distinguished from secondary and tertiary amines.
Tsuji and co-workers reported the use of a palladium catalyst system which gives amination of butadiene with ammonia, Chem. Comm. (Japan), 345 (1971). The reaction is described as taking place in acetonitrile solvent and in the presence of palladium acetate and triphenyl phosphine. However, in the hands of the present inventors, the Tsuji reaction gave only low yields at slow rates.
Recently, in application Ser. No. 697,900, filed June 21, 1976, the present inventors disclosed an improved homogeneous palladium-based catalyst system which facilitates the amination of butadiene with either ammonia or amines with excellent yields and rates under mild conditions. These catalysts, however, give long chain secondary and tertiary octadienyl amines as a result of multiple alkylation of ammonia and telomerization of butadiene. The relatively shorter chain butenylamines desired herein were not produced by the catalyst system.
Preparation of the shorter chain butenylamines by reaction of primary and secondary amines with butadiene using a preformed palladium-diphosphine complex catalyst has been described by Takahashi et al., Bull. Chem. Soc. Japan 45, 1183-91 (1972). However, the reactivity of the amine reactants is reported to be associated with the amine basicity, with the more strongly basic amines being more active. No disclosure of the more weakly basic ammonia is provided by Takahashi. Moreover, the Takahashi reaction requires use of a co-catalytic amount of phenol to provide a suitable reaction rate.